The present invention relates to a coupling apparatus transmitting a rotating force of a first rotary shaft to a second rotary shaft. Further, the present invention relates to a motor device provided with the first rotary shaft, the second rotary shaft and the coupling apparatus, and a wiper motor device for driving a wiper.
Japanese Laid-Open Patent Publication No. 2006-94693 discloses a motor device provided with a motor portion, and a speed reducing portion coupled to the motor portion. Japanese Utility Model No. 2515645 discloses a coupling apparatus for coupling a rotary shaft in a motor portion to a worm shaft in a speed reducing portion.
The coupling apparatus is provided with a first coupling member, a second coupling member, and a damper member. The damper member made of a rubber is arranged between the first coupling member coupled to the rotary shaft, and the second coupling member coupled to the worm shaft. The first coupling member has a discoid main body, and three first arms extending toward the second coupling member from the main body. The second coupling member is formed in the same shape as the first coupling member, and has three second arms. The damper member has a ring-shaped core portion, and six buffering teeth protruding radially outward from the core portion. Three first arms and three second arms are alternately arranged in six buffering recesses defined by six buffering teeth. In other words, the first arm and the second arm face each other in a circumferential direction while holding the buffering teeth therebetween.
A gear housing in the speed reducing portion has an accommodating hole (an axial hole) having a circular cross-sectional shape and accommodating the coupling apparatus. A rotation of the first coupling member is transmitted to the second coupling member via the damper member. As a result, the worm shaft is rotated. The damper member absorbs a deflection and an eccentricity between the rotary shaft and the worm shaft.
The first arms and the second arms compress the buffering teeth in the circumferential direction. Accordingly, there is a risk that the buffering teeth having elasticity are deformed, protrudes radially outward than the first arms and are in contact with the inner circumferential surface of the accommodating hole. In other words, there is a risk that the rotation of the first coupling member and the second coupling member is hindered.
The diameter of the accommodating hole may be enlarged in such a manner as to prevent the buffering teeth from being in contact with the inner circumferential surface of the accommodating hole even if the buffering teeth protrude radially outward. However, if the diameter of the accommodating hole is enlarged, there is a risk that a lubricating agent such as grease or the like applied to the worm shaft passes through the accommodating hole so as to make an intrusion into the motor portion. Accordingly, it is difficult to control the diameter of the accommodating hole.